This invention relates to a vacuum insulating glass (IG) unit, and a method of making the same.
Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, 5,891,536 and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
Prior art FIGS. 1-2 illustrate a conventional vacuum IG unit. IG unit 1 includes two spaced apart sheets of glass 2 and 3 which enclose an evacuated or low pressure space therebetween. Glass sheets 2 and 3 are interconnected by peripheral or edge seal of fused solder 4 and an array of support pillars 5.
Pump out tube 8 is hermetically sealed by solder glass 9 to an aperture or hole 10 which passes from an interior surface of glass sheet 2 to the bottom of recess 11 in the exterior face of sheet 2. A vacuum is attached to pump out tube 8 so that the interior cavity between sheets 2 and 3 can be evacuated to create a low pressure area. After evacuation, tube 8 is melted to seal the vacuum. Recess 11 retains melted and sealed tube 8. Chemical getter 12 may optionally be included within machined recess 13.
Conventional vacuum IG units, with their fused solder glass peripheral seals 4, have been manufactured as follows when the upper glass sheet is slightly smaller in dimension is than the lower sheet. Solder glass is initially deposited around the periphery of the IG unit in an L-shaped step or corner that is formed by virtue of the upper sheet being slightly smaller in dimension than the lower sheet (not shown in FIGS. 1-2). The entire assembly including sheets 2, 3 and the solder glass seal material is then heated to a temperature of approximately 500xc2x0 C. at which the solder glass melts, wets the surfaces of the glass sheets, and flows into the space between the sheets forming hermetic peripheral seal 4. This approximate 500xc2x0 C. temperature is maintained for from about one to eight hours (it has recently been found-that a time of about eight hours at approximately this temperature is preferred to properly bond solder glass seal material to the glass substrate(s)). After formation of peripheral/edge seal 4 and of the seal around pump out tube 8, the assembly is cooled to room temperature.
Unfortunately, these 500xc2x0 C. temperatures and multi-hour periods over which such temperatures are maintained in forming edge seal 4 are undesirable, especially when it is desired to use a tempered glass sheet in the IG unit. Tempered glass loses temper strength upon exposure to high temperatures as a function of heating time as shown in FIGS. 3-4. Moreover, high temperatures may have an adverse effect upon certain low-E coating(s) that may be applied to one or both of the glass sheets.
FIG. 3 is a graph illustrating how fully thermally tempered plate glass loses original temper upon exposure to different temperatures for different periods of time, where the original center tension stress is 3,200 MU per inch. The X-axis in FIG. 3 is exponentially representative of time in hours (from 1 to 1,000 hours), while the Y-axis is indicative of the percentage (%) of original tempering strength remaining after exposure. FIG. 4 is a graph similar to FIG. 3, except that the X-axis extends from 0 to 1 hour exponentially.
Seven different curves are illustrated in FIG. 3, each indicative of a different temperature exposure in degrees Fahrenheit (F). The different temperature curves/lines are 400xc2x0 F. (across the top of the FIG. 3 graph), 500xc2x0 F., 600xc2x0 F., 700xc2x0 F., 800xc2x0 F., 900xc2x0 F., and 950xc2x0 F. (the bottom curve of the FIG. 3 graph). A temperature of 900xc2x0 F. is equivalent to approximately 482xc2x0 C., which is within the range utilized for forming the aforesaid conventional solder glass peripheral seal/joint 4. Thus, attention is drawn to the 900xc2x0 F. curve in FIG. 3, labeled by reference numeral 18. As shown, only 20% of the original temper remains after one hour at this temperature (900xc2x0 F. or 482xc2x0 C.). Such a loss of temper strength may result in certain window units not being able to pass safety codes set for environments where tempered glass is desirable.
Still referring to FIGS. 3-4, it is noted that much better temper strength remains in a thermally tempered glass sheet when it is heated to a temperature of 800xc2x0 F. (i.e. about 428xc2x0 C.) for one hour (as opposed to 900xc2x0 F. for one hour). Such a glass sheet retains about 70% of its original temper strength after one hour at 800xc2x0 F. which is significantly better than the less than 20% when at 900xc2x0 F. for the same period of time.
It is apparent from the above that there exists a need in the art for a vacuum IG unit, and corresponding method of making the same, where a hermetic seal may be provided between opposing glass sheets without thermally tempered glass sheet(s) of the unit losing more than about 50% of their original temper strength. There also exists a need in the art for a vacuum IG unit including tempered glass sheets, wherein the peripheral seal is formed such that the glass sheets retain more of their original temper strength than with conventional vacuum IG manufacturing techniques. There also exists a need in the art to decrease post-tempering processing time, and to reduce the approximate 8 hour period which is now believed to be necessary to properly cause edge seal solder glass material to diffuse into or bond to glass substrate(s). It is a purpose of this invention to fulfill any and/or all of the above listed needs in the art.
This invention will now be described with respect to certain embodiments thereof, accompanied by certain illustrations.
An object of this invention is to provide a vacuum IG unit having a peripheral or edge seal, wherein the peripheral/edge seal is formed so that thermally tempered glass sheets of the unit retain more of their original temper strength than if conventional seal forming techniques were used with the same seal material.
Another object of this invention is to provide a vacuum IG unit (and method of making the same), wherein the resulting thermally tempered glass sheet(s) retain at least about 50% of their original temper strength after formation of the unit.
An object of this invention is to provide an edge seal for a vacuum IG unit, wherein the edge seal does not require processing temperatures greater than about 450xc2x0 C. other than during tempering.
Yet another object of this invention is to, in the manufacture of a vacuum IG unit, provide or deposit at least an initial portion of the edge seal on one or both of the glass substrates prior to temper, and thereafter use the heat in the tempering furnace/oven to cause the initial edge seal portion to diffuse into or bond to the glass during tempering. In certain embodiments, this permits lower processing temperatures to be used thereafter to form the peripheral/edge seal because higher temperatures are typically needed to cause solder glass seal material to diffuse into or bond to glass substrate(s) than are needed to cause such material to bond to another piece of the same material.
Another object of this invention is to reduce the amount of post-tempering heating time necessary to form a peripheral/edge seal in a vacuum IG unit.
Another object of this invention is to reduce post-tempering maximum temperatures needed to form a peripheral/edge seal in a vacuum IG unit.
Another object of this invention is to fulfill any and/or all of the above-listed objects.
Generally speaking, this invention fulfills any or all of the above described needs by providing a method of making a window unit comprising the steps of:
providing first and second glass substrates;
providing a first seal material portion on at least one of the substrates;
thermally tempering the at least one substrate with the first seal material portion thereon;
following said tempering step, providing a plurality of spacers between the first and second substrates;
heating the first seal material portion to a seal forming temperature less than a maximum temperature achieved during said tempering step in forming a seal that defines a sealed space between the substrates; and
causing the sealed space to be at a pressure less than atmospheric pressure.
This invention further fulfills any or all of the above described needs by providing a method of making a window unit comprising the steps of:
providing first and second glass substrates;
providing a first seal material portion on at least one of the substrates;
thermally tempering the at least one substrate with the first seal material portion thereon, said tempering step including heating the at least one substrate to a temperature of at least about 535xc2x0 C.;
following said tempering step, providing at least one spacer between the first and second substrates; and
heating the first seal material portion to a seal forming temperature of less than about 450 degrees C. in a post-tempering heating step in forming a seal that defines a sealed space between the substrates.
This invention still further fulfills any or all of the above described needs in the art by providing an insulating is glass (IG) window unit comprising:
first and second glass substrates spaced from one another so as to define-a low pressure space therebetween, said low pressure space having a pressure less than atmospheric pressure; and
a hermetic seal disposed between said substrates sealing said low pressure space from surrounding atmosphere so as to maintain pressure less than atmospheric pressure in said space, and wherein at least a portion of said-hermetic seal bonds to one of said substrates during thermal tempering of said one of said glass substrates.